python中for循环常见的语法错误

python中for循环常见的语法错误

python中，for循环对于执行同类的操作非常有用。然而在使用for循环的过程中，即使是python高手也可能会犯一些常见的语法错误问题。庆幸的是，这种错误并不难排查出来。

9python中for循环遍历列表的几种方法

对于位于for语句后面，属于循环组成部分的代码，需要使用缩进。如果忘记缩进，会报错。代码示例如下：

cities = ["Guangzhou","Beijing","Shanghai","Nanjing"]

for city in iter(cities):

print(city)

上述代码中，for循环后的语句并没有缩进。正确的代码如下：

cities = ["Guangzhou","Beijing","Shanghai","Nanjing"]

for city in iter(cities):

print(city)

如下图，根据代码的逻辑可以看出，我们希望对列表里的每个元素进行遍历，遍历后输出2句话。但第2个print语句没有进行缩进。代码示例如下：

cities = ["Guangzhou","Beijing","Shanghai","Nanjing"]

for i in range(len(cities)):

print("第"+ str(i+1)+ "个城市是：")

print(cities[i])

在使用for循环中，正确的做法应该是保证for循环包含的语句全部使用缩进。正确代码如下：

cities = ["Guangzhou","Beijing","Shanghai","Nanjing"]

for i in range(len(cities)):

print("第"+ str(i+1)+ "个城市是：")

print(cities[i])

通常我们在使用for循环进行了一系列操作后，最后会将循环的结果做总结或者输出整个循环的结果。如下图中的代码，虽然系统没有报错，但并没有很好的得到这个结果。代码示例如下：

cities = ["Guangzhou","Beijing","Shanghai","Nanjing"]

for i in range(len(cities)):

print("第"+ str(i+1)+ "个城市是：")

print(cities[i])

print("In conclusion, here are 4 cities in the list.")

如上所述的总结性的语言应该是放在整个循环结束后的，所以不需要缩进。正确代码如下：

cities = ["Guangzhou","Beijing","Shanghai","Nanjing"]

for i in range(len(cities)):

print("第"+ str(i+1)+ "个城市是：")

print(cities[i])

print("In conclusion, here are 4 cities in the list.")

for循环中，for语句末尾的冒号是必不可少的，它告诉python，下一行开始是for循环包含的内容。示例代码如下：

cities = ["Guangzhou","Beijing","Shanghai","Nanjing"]

for i,city in enumerate(cities)

print(i+1,city)

正确的代码如下：

cities = ["Guangzhou","Beijing","Shanghai","Nanjing"]

for i,city in enumerate(cities):

print(i+1,city)